Intervertebral disc augmentation and rehydration with superabsorbent polymers

ABSTRACT

The embodiments provide a method for treating an intervertebral disc having a nucleus pulposus and an annulus fibrosis, using one or more superabsorbent polymers. Additionally, the embodiments provide a method for bulking up an intervertebral disc having a nucleus pulposus and an annulus fibrosis, using one or more superabsorbent polymers. The methods comprise introducing an amount of the superabsorbent polymers into the intervertebral disc space without removing nucleus pulposus or annulus fibrosis material.

FIELD OF THE INVENTION

Embodiments relate to apparatus, methods, and devices for augmentationof the intervertebral disc space. More specifically, embodiments relateto methods of using superabsorbent polymers to treat an intervertebraldisc space.

BACKGROUND

The intervertebral disc functions to stabilize the spine and todistribute forces between vertebral bodies. The intervertebral disc iscomposed primarily of three structures: the nucleus pulposus, theannulus fibrosis, and two vertebral end-plates. These components worktogether to absorb the shock, stress, and motion imparted to the spinalcolumn. The nucleus pulposus is an amorphous hydrogel in the center ofthe intervertebral disc. The annulus fibrosis, which is composed ofhighly structured collagen fibers, surrounds and constrains the nucleuspulposus within the center of the intervertebral disc. The vertebralend-plates, composed of hyalin cartilage, separate the disc fromadjacent vertebral bodies and act as a transition zone between the hardvertebral bodies and the soft disc.

The nucleus pulposus typically contains a negatively chargedproteoglycan component. Proteoglycans are glycoproteins with manypolysaccharide side chains, and have properties that are more liketypical polysaccharides than proteins. The proteoglycan component of thenucleus pulposus associates with water to form a hydrated gel. Water mayreach the nucleus pulposus from sieve-like pores in the end plates. Theresulting osmotic pressure within the intervertebral disc causes it toexpand axially (i.e., vertically), driving the adjacent vertebrae apart.On the other hand, mechanical movements resulting in axial compression,flexion, and rotation of the vertebrae exert forces on theintervertebral disc, which tends to drive water out of the nucleuspulposus. Water movement into and out of an intervertebral disc underthe combined influence of osmotic gradients and mechanical forces isimportant for maintaining disc health. In a normal healthy nucleuspulposus, water comprises between about 80% to about 90% of thenucleus's total weight.

Intervertebral discs may be displaced or damaged due to trauma, disease,and the normal aging process. Intervertebral discs undergoingdegeneration typically experience dehydration relatively early in thedegeneration process. During dehydration of the intervertebral disc, thewater associated with the proteoglycan hydrogel comprising the nucleuspulposus of the disc may be lost. Dehydration of the nucleus may resultin collapse of the disc space and reduced disc space height. Reduceddisc space height may lead to instability of the spine, decreasedmobility, and back and leg pain.

Several general strategies have been proposed in order to restore discheight in a dehydrated intervertebral disc. In one strategy, the disc istreated by inducing repair or regeneration of the nucleus with abiological treatment. Biological treatments include a broad variety oftreatment regimens such as the implantation of nucleus pulposus cellsharvested from healthy intervertebral discs, steroidal injections toinduce cell proliferation, genetic treatments to induce and/or increaseproteoglycan production by the pulposus cells, and so forth.Unfortunately, effective biological treatments appear to be many yearsaway from commercial development and routine use.

In another strategy to treat dehydrated intervertebral discs, a portionor all of the nucleus is removed and a prosthetic nucleus device isimplanted in the intervertebral disc space to augment or completelyreplace the dehydrated nucleus. Alternatively, a total disc replacement(“TDR”) operation may be performed wherein not just the dehydratednucleus but the entire intervertebral disc is removed and replaced witha prosthesis. However, nucleus and TDR replacements remain unproven.Also, even when minimally invasive surgical techniques are used, thesesurgeries are relatively difficult to perform and inflict a good deal oftrauma on the patient, resulting in increased post-surgical recoverytimes and disability. Additionally, the complexity of currentlyavailable intervertebral prostheses necessitates careful and meticulousconsideration of the patient's unique prognosis to determine whichprosthesis is most likely to result in a positive therapeutic outcome.

The description herein of problems and disadvantages of knownapparatuses, methods, and devices is not intended to limit theembodiments to the exclusion of these known entities. Indeed,embodiments may include one or more of the known apparatus, methods, anddevices without suffering from the disadvantages and problems notedherein.

BRIEF SUMMARY

What is needed is an improved method to treat an intervertebral disc. Inparticular, what is needed is a relatively simple, fast, and easy methodto treat a dehydrated intervertebral disc. Furthermore, what is neededis a method to treat dehydrated intervertebral discs that is minimallyinvasive and easily reversible relative to other treatment regimens.

Therefore, in accordance with one embodiment, there is provided a methodfor treating an intervertebral disc using one or more superabsorbentpolymers. The intervertebral disc has a nucleus pulposus and an annulusfibrosis. The method comprises introducing the superabsorbent polymersinto the intervertebral disc space without removing nucleus pulposus orannulus fibrosis material, thereby rehydrating the intervertebral disc.

In accordance with another embodiment, there is provided a method forbulking up an intervertebral disc using one or more superabsorbentpolymers. The intervertebral disc has a nucleus pulposus and an annulusfibrosis. The method comprises introducing the superabsorbent polymersinto the intervertebral disc space without removing nucleus pulposus orannulus fibrosis material, thereby maintaining and/or increasing thedisc height, the disc volume, or the intra-discal pressure.

These and other features and advantages will be apparent from thedescription provide herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, embodiments A, B, and C, illustrates an exemplary “wet” deliverymethod for introducing superabsorbent polymers to the intervertebraldisc space.

FIG. 2, embodiments A, B, C, and D, illustrates an exemplary “dry”delivery method for introducing superabsorbent polymers to theintervertebral disc space.

FIG. 3, embodiments A and B, illustrates an exemplary inflatable memberto which a superabsorbent polymer is delivered to treat anintervertebral disc space.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is intended to convey a thorough understandingof the various embodiments by providing a number of specific embodimentsand details involving treatment of the intervertebral disc space. It isunderstood, however, that the embodiments are not limited to thesespecific preferred descriptions and details, which are exemplary only.It is further understood that one possessing ordinary skill in the art,in light of known systems and methods, would appreciate the use of theembodiments for their intended purpose and benefits in any number ofalternative embodiments.

As used herein and in the appended claims, the singular forms “a,” “an,”and “the” include plural reference unless the context clearly dictatesotherwise. Thus, for example, a reference to “a superabsorbent polymer”includes a plurality of such polymers, and a reference to “apolyelectrolyte” is a reference to one or more polyelectrolytes, and soforth.

As used herein, the term “polyelectrolytes” refers to long linear chainsof polymers with ionic groups along the molecular chains. Thepolyelectrolytes may or may not also have side chains on the polymers.Because of the presence of the ionic groups, polyelectrolytes attractwater (i.e., are hydrophilic) and then eventually dissolve when placedin sufficiently large quantities of water. Polyelectrolytes are, atmost, only slightly crosslinked.

The expression “superabsorbent polymers” (“SAPs”) refers to generallywater-insoluble but water-swellable polymeric substances capable ofimbibing, absorbing, or gelling extremely large amounts of fluids, suchas water and aqueous solutions. Typically, superabsorbent polymers areproduced by crosslinking hydrophilic polymers. Because of theircrosslinked hydrophilic polymer structure, superabsorbent polymersabsorb fluids without dissolving into solution. An exemplary type ofsuperabsorbent polymer is crosslinked polyelectrolytes.

In a preferred embodiment, superabsorbent polymers are capable ofabsorbing fluids in an amount that is at least ten times the weight ofthe SAPs in their dry form, at atmospheric pressure. In anotherpreferred embodiment, superabsorbent polymers are capable of absorbingfluids in an amount that is at least twenty times the weight of the SAPsin their dry form, at atmospheric pressure. In still another preferredembodiment, superabsorbent polymers are capable of absorbing fluids inan amount that is at least twenty-five times the weight of the SAPs intheir dry form, at atmospheric pressure. The fluid is taken into themolecular structure of the superabsorbent polymer and not simplycontained in pores from which it can be expressed by squeezing.

The water absorption and water retention characteristics ofsuperabsorbent polymers are due to the presence in the polymer structureof ionizable functional groups. For example, some carboxylated,phosphonoalkylated, sulphoxylated, and phosphorylated polymers areuseful as superabsorbent polymers. The ionizable functional groups maybe left in their free acid or base forms (i.e., “underneutralizedsuperabsorbent polymers” or “uSAPs”), or else may be neutralized toyield the salt form of the groups.

Preferably, the ionizable functional groups undergo dissociation uponcontact with water. In the dissociated state, the superabsorbent polymerchains may have a series of functional groups attached to it whichgroups have the same electric charge and thus repel one another. Thismay lead to expansion of the superabsorbent polymer structure which, inturn, permits further absorption of water molecules. This expansion,however, is subject to the constraints provided by the cross-links inthe superabsorbent polymer structure, which are sufficient to preventdissolution of the SAP.

The degree of cross-linking of superabsorbent polymers can be animportant factor in establishing their absorbent capacity and gelstrength. Absorbent polymers useful in the embodiments described hereinpreferably have adequately high sorption capacity, and relatively lowgel strength compared to the hydrogels used in nucleus andintervertebral disc replacement devices. Gel strength relates to thetendency of the swollen polymer to deform under an applied stress. A lowgel strength may be desirable because the retained, or original, nucleuspulposus and annulus fibrosis of the intervertebral disc may be intendedto provide the majority of the strength in the intervertebral disc. Thesuperabsorbent polymers, in comparison, may be intended to offer littleor no structural strength to the intervertebral disc, other than thatprovided by the SAPs' ability to rehydrate the disc and the bulkingeffect of introducing the SAPs to the disc space.

In a preferred embodiment, the superabsorbent polymers are no more thanabout 30% crosslinked. In another preferred embodiment, thesuperabsorbent polymers are not more than about 20% crosslinked. Instill another preferred embodiment, the superabsorbent polymers are notmore than about 10% crosslinked. In these embodiments, the relativelylow percentage of crosslinked polymer chains ensures that thesuperabsorbent polymers are weak and do not provide substantialmechanical strength to the intervertebral disc, other than the strengthprovided by the SAPs' ability to absorb fluids and rehydrate the discspace. Additionally, the low crosslinking of the superabsorbent polymershelps to ensure that the polymers are able to expand and absorb largeamounts of water.

The superabsorbent polymers may be lightly crosslinked by including theappropriate amount of a suitable crosslinking monomer duringpolymerization of the constituent polymer chains. Alternatively, thepolymer chains comprising the superabsorbent polymers may be crosslinkedafter polymerization of the chains by reaction with a suitablecrosslinking agent. Examples of crosslinking agents include, but are notlimited to:

(i) polyfunctional ethylenically unsaturated cross-linking agents suchas N,N′-methylenebisacrylamide, polyethylene glycol di(meth)acrylate,trimethylolpropane tri(meth)acrylate, and divinyl benzene;

(ii) polyfunctional cross-linking agents such as epichlorohydrin andrelated halo epoxy compounds, diglycidyl ether compounds, diisocyanates,polyaldehydes, and polyfunctional amines and imines;

(iii) triallylamine, diaziridine compounds, acrylic acid, diiodopropane,dichloropropane, ethylene glycol diglycidyl ether,alkylenebisacylamides, di- and poly-halogenated compounds, and di- orpoly-epoxy compounds; and

(v) mixtures and combinations thereof.

Superabsorbent polymers may include polymer chains that are synthetic,natural, and hybrid synthetic-natural polymers. Natural polymers includepolysaccharides such as cellulose, starch, and regenerated cellulosethat are modified to be carboxylated, phosphonoalkylated, sulphoxylatedor phosphorylated, thereby causing the polymer chains to become highlyhydrophilic. Synthetic polymers include, but are not limited to,polyacrylates. U.S. Pat. No. 5,147,343 issued to Kellenberger, U.S. Pat.No. 4,673,402 issued to Weisman, U.S. Pat. No. 5,281,207 issued toChmielewski et al., and U.S. Pat. No. 4,834,735 issued to Alemany, etal. disclose many types of SAPs and methods for making them, and areincorporated herein by reference in their entirety in accordance withthe described embodiments.

Some exemplary superabsorbent polymers may include, but are not limitedto:

(i) polyacrylic acid, polymethacrylic acid, polymaleic acid, copolymersthereof, and alkali metal and ammonium salts thereof;

(ii) graft copolymers of starch and acrylic acid, starch and saponifiedacrylonitrile, starch and saponified ethyl acrylate, and acrylate-vinylacetate copolymers saponified;

(iii) polyvinylpyrrolidone, polyvinyl alkylether, polyethylene oxide,polyacrylamide, and copolymers thereof;

(iv) copolymers of maleic anhydride and alkyl vinylethers;

(v) saponified starch graft copolymers of acrylonitrile, acrylateesters, vinyl acetate, and starch graft copolymers of acrylic acid,methyacrylic acid, and maleic acid;

(vi) the product of crosslinking acrylamide with backbones ofkappa-carrageenan and soldium alginate using methylenebisacrylamide andpotassium persulfate;

(vii) the product of crosslinking, using a bifunctional crosslinkingreagent, an acyl-modified protein matrix such as soy protein isolatewhich has been acyl-modified by treatment withethylenediaminetetraacetic acid dianhydride; and

(viii) mixtures and combinations thereof.

It is believed that the rehydrated nucleus pulposus functions in amanner that can be analogized to a tire. By increasing the wateraffinity of the intervertebral disc (i.e., introducing a superabsorbentpolymer therein) it is thought that the hydrodynamic pressure inside ofthe disc space may be increased. The water inside of the disc is likethe air inside of a tire, and the annulus functions like the tireitself. Increasing the hydrodynamic pressure inside of theintervertebral disc space inflates the disc. The load placed on the discis carried by the annulus, which preferably is sufficiently healthy,intact, and competent to retain the water, superabsorbent polymers, andnucleus tissue inside of the disc space. Therefore, it is thought thatthe superabsorbent polymers, when delivered to the disc space, bearlittle, if any, of the load of the intervertebral disc. Instead, it isthought that the annulus fibrosis and rehydrated nucleus pulposus bearthe majority of the load of the disc, as would occur in a normal,healthy disc. Thus, the superabsorbent polymers may not and preferablydo not need a high degree of structural strength.

Because the superabsorbent polymers act to attract and maintain water inthe disc space, and thereby rehydrate the nucleus pulposus, it isdesirable that healthy annulus fibrosis and endplates be present in theintervertebral disc. Otherwise, delivery of a superabsorbent polymer tothe intervertebral disc may not result in the desired level ofrehydration and augmentation. In particular, a compromised annulusfibrosis or endplate may not be capable of retaining the water that isattracted to the superabsorbent polymer, the superabsorbent polymeritself, and the nucleus tissue. Therefore, in the case of asignificantly compromised annulus fibrosis or endplate, little or norehydration of the nucleus may occur even after introduction of asuperabsorbent polymer to the disc space.

Therefore, the methods provided by the embodiments herein preferably areused to treat patients with mild to moderate disc degeneration and anessentially intact and competent annulus fibrosis. As explained herein,delivery of the superabsorbent polymers may be accomplished with littleor no additional injury to the annulus fibrosis. The methods providedherein may be especially useful for patients that are not goodcandidates for nucleus replacement surgery, spinal fixation, total discreplacement, spinal fusion, and other surgical regimens for thetreatment of degenerated intervertebral discs.

Accordingly, embodiments provide a method for treating an intervertebraldisc having a nucleus pulposus and an annulus fibrosis, using one ormore superabsorbent polymers. The method comprises introducing thesuperabsorbent polymers into the intervertebral disc space withoutremoving nucleus pulposus or annulus fibrosis material, therebyrehydrating the intervertebral disc. The intervertebral disc may be acervical, lumbar, or thoracic disc.

Furthermore, embodiments provide a method for bulking up anintervertebral disc having a nucleus pulposus and an annulus fibrosis,using one or more superabsorbent polymers. The method comprisesintroducing the superabsorbent polymers into the intervertebral discspace without removing nucleus pulposus or annulus fibrosis material,thereby increasing the height, the volume, and/or the intra-discalpressure of the disc. The intervertebral disc may be a cervical, lumbar,or thoracic disc.

Preferably, the methods provided herein are used to rehydrate theintervertebral disc until equilibrium swelling is attained.Additionally, the methods may be useful to treat an intervertebral discthat already has at least partially collapsed. Preferably, the amount ofsuperabsorbent polymer placed in the intervertebral disc is sufficientto increase the disc height, and more preferably to restore the disc'snatural height. Skilled artisan will be capable of determining thedesired amount of superabsorbent polymer based on a number of factors,including, for example, the degree of disc degeneration, the age,weight, and health of the patient, and the degree of restorationrequired. Additionally, the methods provided herein may be used to slowthe rate of progressive collapse of an intervertebral disc and/ormaintain the height of an intervertebral disc experiencing progressivecollapse.

The superabsorbent polymers may be delivered to the disc space in avariety of forms, such as beads, fibers, flakes, granules, microspheres,nano-particles, particles, pellets, platelets, powder, randomly shapedparticles, rods, chunks, pieces, and so forth. Preferably, whatever formthe superabsorbent polymers are in, the largest dimension of thesuperabsorbent polymer is not more than about 5 mm, more preferably nomore than about 2 mm, and most preferably no more than about 1 mm. Thesuperabsorbent polymers may be delivered to the intervertebral discspace, for example, utilizing “dry” and “wet” delivery methods.

In the “wet” delivery method, the superabsorbent polymers may befluidized, for example, by mixing the superabsorbent polymers with amedium to form a gel, suspension, paste, solution, mixture, etc. of thesuperabsorbent polymers that is sufficiently fluid in nature to bedelivered through a needle, catheter, trocar, cannula, syringe, caulkgun-like device, barrel-plunger device, other injection or extrusiondevices, or any other such applicable delivery device. For example, thedelivery device may be used to pierce or puncture the annulus fibrosisin order to reach the interior of the disc space and nucleus pulposus.If desired, a more rigid, larger diameter cannula may be used to gainaccess to the outer disc annulus, and a smaller diameter needle may beused to puncture the annulus and inject the superabsorbent polymer intothe disc space. Additionally, if desired, a more rigid instrument suchas a stylet may be used to guide the delivery device through the bodyand towards the disc space.

The flowable superabsorbent polymers (e.g., a superabsorbentpolymer-containing gel or suspension) may be introduced into thedelivery device and subjected to pressure or mechanical forces in orderto force the superabsorbent polymers to exit the distal end of thedelivery device and enter the intervertebral disc space. In an exemplaryembodiment, a syringe filled with the superabsorbent polymer in the formof a gel, suspension, paste, solution, mixture, etc. may be used toforce the superabsorbent polymer through the delivery device (e.g., aneedle, cannula, catheter, trocar, etc.) and into the disc space.

It may be desirable to place the patient under traction in order toreduce intra-discal pressure before, during, and after injection. Italso may be desirable to distract the upper and lower vertebral bodiesusing a minimally-invasive disc distraction device or external tractiondevices. This may be advantageous in order to reduce the injectionpressure necessary to affect delivery of the superabsorbent polymer,increase the injectable volume of the disc space, reduce the potentialfor post-delivery leakage of the superabsorbent polymer, and so forth.When sufficient superabsorbent polymer has been introduced into the discspace, the delivery device may be removed.

Fluids for delivery of the superabsorbent polymers to the disc spaceinclude, but are not limited to: water, saline, vegetable oils (e.g.,canola, corn, and peanut oil), olive oil, alcohols, triacetin, diacetin,tributyrin, triethyl citrate, tributyl citrate, acetyl triethyl citrate,acetyl tributyl citrate, triethylglycerides, glycerin, triethylphosphate, diethyl phthalate, diethyl tartrate, mineral oil, polybutene,silicone fluid/oil, glylcerin, ethylene glycol, polyethylene glycol,octanol, ethyl lactate, propylene glycol, propylene carbonate, ethylenecarbonate, butyrolactone, ethylene oxide, propylene oxide,N-methyl-2-pyrrolidone, 2-pyrrolidone, glycerol formal, methyl acetate,ethyl acetate, methyl ethyl ketone, dimethylformamide, dimethylsulfoxide (DMSO), tetrahydrofuran, caprolactam, decylmethylsulfoxide,oleic acid, 1-dodecylazacycloheptan-2-one, and mixtures and combinationsthereof.

Preferably, the delivery device is of a small cross-section so that nolarger a defect than is necessary is created in the annulus fibrosis orendplate when it is pierced. This is desirable because it is thoughtthat the annulus fibrosis is slow to heal, and a puncture in the annulusmay allow fluids to escape from the intervertebral disc space.Therefore, it is may be desirable that the flowable superabsorbentpolymer not experience significant swelling prior to delivery to thedisc space. For example, if the superabsorbent polymer is in a granularform, significant swelling of the superabsorbent polymer grains whenthey are mixed with a medium to fluidize them may prevent the flowablesuperabsorbent polymer from being capable of passing through asmall-diameter needle or catheter. This, in turn, would necessitate theuse of a larger-diameter needle or catheter to deliver the flowablesuperabsorbent polymer, and result in greater damage to the annulusfibrosis.

Thus, it may be desirable to fluidize the superabsorbent polymer withnon-aqueous fluids or a mixture of non-aqueous and aqueous fluids. Doingso may reduce the superabsorbent polymer's viscosity so that it issufficiently flowable to facilitate introduction to the disc space, butwithout causing pre-delivery swelling of the superabsorbent polymer.

The delivery of a flowable superabsorbent polymer is exemplarilyillustrated in FIG. 1, embodiments A, B, and C. In embodiment A, asyringe/needle assembly 10 is provided as a delivery device with asuperabsorbent polymer 11 that has been mixed with a fluid, eitheraqueous and/or non-aqueous. In embodiment B, the syringe/needle assembly10 penetrates the annulus fibrosis 13 of the intervertebral disc space16 having end plates 12 a and 12 b. In the preferred embodiment depictedin FIG. 1, embodiment B, the distal end of the syringe/needle assembly10 is inserted into the nucleus pulposus 14 of the disc for directdelivery of the superabsorbent material. The syringe is depressed toexpel the superabsorbent material 15, as shown in embodiment C, and thenremoved from the disc space. Optionally, the annulus fibrosis may betreated to heal any injury incurred due to the insertion of the syringe,as explained herein.

In one embodiment, the superabsorbent polymers that are used to augmentand rehydrate the intervertebral disc comprise polyelectrolytes. Becauseof the presence of ionizable groups in polyelectrolytes, it is thoughtthat the capacity of polyelectrolytes to absorb and/or attract water andother aqueous mediums may be sensitive to factors such as the pH of theaqueous medium, ionic strength of the aqueous medium, electric fields,and temperature. Desirably, these variables may be adjusted in order toaffect the behavior of the polyelectrolytes, especially the behavior ofcrosslinked polyelectrolytes that comprise a flowable superabsorbentpolymer that is to be delivered to the intervertebral disc space.Preferably, these variables may be adjusted in order to reduce thevolume of the superabsorbent polymer-containing gel or solution in orderto facilitate delivery of the superabsorbent polymers throughsmall-diameter needles and catheters.

For example, a lower pH aqueous medium may be mixed with thepolyelectrolyte-comprising superabsorbent polymers prior to delivery tothe disc space. Because the lower pH aqueous medium may reduceionization of the polyelectrolytes, it may reduce the polyelectrolytes'affinity for water. Thus, the superabsorbent polymer may have less of atendency to swell when combined with a low-pH medium to fluidize thesuperabsorbent polymer prior to delivery to the disc space. A decreasedtendency to swell may be desirable in order to deliver thesuperabsorbent polymer through a small-diameter needle or catheter.

The ionic strength of the medium that is used to fluidize thepolyelectrolyte-comprising superabsorbent polymer for delivery to thedisc space also may be adjusted in order to discourage swelling of thepolyelectrolytes prior to introduction into the disc space. For example,a hypertonic saline medium or a medium with a high concentration ofionic salts may be used to fluidize the superabsorbent polymer withoutinducing significant swelling of the polyelectrolytes. After insertion,the saline or salt medium may diffuse out of the disc and be replacedwith body fluids, which may dilute the saline or salt medium and reduceits ionic strength. The superabsorbent polymer then can absorb thelowered-ionic strength medium, leading to rehydration of the nucleus.

In another embodiment, an electric field may be used to reduce thepolyelectrolytes' ability to ionize in solution, and thus reduce theiraffinity for water, during delivery to the disc space. Again, this maybe useful in order to reduce the swelling of thepolyelectrolyte-comprising superabsorbent polymer during delivery to thedisc space, thereby facilitating delivery of the superabsorbent polymerthrough a small-diameter needle or catheter. After delivery to the discspace, the electric field may be removed to restore the superabsorbentpolymer's ability to ionize, and thus its affinity for water.

Finally, the temperature of the polyelectrolyte-comprisingsuperabsorbent polymer and the temperature of the medium used tofluidize it may be adjusted in order to decrease the polyelectrolytes'affinity for water during delivery to the disc space. Adjustment ofthese four variables (pH, ionic strength, electric fields, andtemperature) to reduce the polyelectrolyte-comprising superabsorbentpolymer's hydrophilicity during delivery to the disc space may beespecially desirable when the superabsorbent polymer is in acomparatively bulky, solid form (e.g., microspheres).

Another way in which the superabsorbent polymers may be delivered to thedisc space is via a “dry” delivery method, without rendering thesuperabsorbent polymer flowable. According to the dry delivery method,the superabsorbent materials may be packed into a small diameterdelivery device such as a needle, catheter, trocar, cannula, etc. in theform of a dry powder, particulates, small chunks, pellets, short rods,chunks, pieces, and so forth. No fluid is mixed with the superabsorbentmaterials prior to delivery to the intervertebral disc space.Preferably, the delivery device has a diameter of no more than about 3mm, more preferably no more than about 2 mm, and most preferably no morethan about 1 mm.

The annulus fibrosis may be punctured and the delivery device inserted.Preferably, the delivery device itself may be used to puncture theannulus fibrosis, especially when the delivery device is a needle ortrocar. The distal end of the delivery device then may be brought closeto the center of the disc space. A plunger, stylet, or other such devicemay be used to extrude or push the dry superabsorbent polymer materialthrough the delivery device and into the disc space. When sufficientsuperabsorbent polymer material has been delivered to the disc space,the delivery device may be removed.

It is believed that, upon delivery to the intervertebral disc space, thesuperabsorbent polymers will attract water to the disc space untilequilibrium swelling is achieved. Preferably, sufficient superabsorbentpolymer is delivered to the disc space to cause the disc to increase inheight, and more preferably to return to its natural height. In oneembodiment, the superabsorbent polymers may be used to treat adegenerated intervertebral disc that has at least partially collapsed.Introduction of the SAPs to the disc space may cause the height of theat least partially collapsed disc space to increase. In anotherembodiment, the superabsorbent polymers may be used to treat adegenerated intervertebral disc that is experiencing progressive disccollapse. Introduction of the SAPs to the disc that is experiencingprogressive collapse may reduce the rate of collapse. Also, introductionof the SAPs to the disc that is experiencing progressive collapse maymaintain the height of the disc.

In one embodiment, “wet” delivery of the superabsorbent polymer isaccomplished by mixing the polymer material with an aqueous medium suchas water, saline solution, a contrast media containing water, and soforth. The presence of water in the aqueous medium may causepre-delivery swelling of the superabsorbent polymer. After delivery tothe intervertebral disc space, it is thought that the superabsorbentpolymer will either exude water into the disc space and nucleus, or elsewill continue to attract water to the disc space. In either case, it isbelieved that the end result of introducing the superabsorbent polymerto the intervertebral disc space will be to increase the hydrodynamicpressure in the disc space, rehydrate the nucleus, and restore the disc,such as restoring the disc space's natural height, volume, and loadsupport.

In another embodiment, “wet” delivery of the superabsorbent polymer isaccomplished by mixing the superabsorbent polymer material with anon-aqueous medium. It is believed that, because of the superabsorbentpolymers' limited absorption of the non-aqueous medium and limitedswelling, a slurry or suspension may be formed given a sufficient amountof the non-aqueous solution. It also is believed that, after delivery tothe intervertebral disc space, the non-aqueous solution will diffuse outof the disc space and be replaced by water attracted by the highlyhydrophilic superabsorbent polymer. The net result may be increasedwater in the disc space and the attendant beneficial effects thereofthat have been described herein.

In still another embodiment, “wet” delivery of the superabsorbentpolymer is accomplished by mixing the polymer material with a mixture ofnon-aqueous and aqueous mediums. A mixture of non-aqueous and aqueousmediums may be useful where is it desired to deliver the superabsorbentpolymers with minimal pre-delivery swelling, but the superabsorbentpolymers are not sufficiently soluble in purely non-aqueous mediums tobe brought into solution and/or fluidized. Therefore, by mixing asufficient amount of an aqueous medium with the non-aqueous medium, thesuperabsorbent polymers may be brought into solution and fluidized butwith a minimal amount of pre-delivery swelling. The ratio of non-aqueousto aqueous mediums in the mixture may depend upon the type ofsuperabsorbent polymer(s) and fluid mediums that are to be used.

In an alternative embodiment, the superabsorbent polymers may beconsolidated into a substantially dehydrated solid device that isdelivered to the disc space. Preferably, the solid device is deliveredin the form of an elongated shape with as small a cross-section aspossible (e.g., small diameter rods no more than about 1 mm in diameter)in order to facilitate delivery to the disc space through a smalldefect, puncture, or hole in the annulus fibrosis. Also, thesuperabsorbent solid devices preferably dissolve in vivo to releasetheir constituent superabsorbent polymers into the disc space in orderto rehydrate the nucleus.

The solid device may comprise a plurality of unconsolidated particles.In a further embodiment, the solid device may comprise a binder.Preferably, the binder is a bioresorbable polymer that degrades in vivoand releases the superabsorbent polymer. The binder may be mixed withthe superabsorbent polymers and then heated and/or pressed to form theshaped solid device. Exemplary binders that may be used in accordancewith the embodiments described herein include:

(i) non-resorbable polymers such as poly(urethanes), poly(siloxanes},poly(methyl methacrylate), poly(ethylene), poly(vinyl alcohol,poly(vinyl pyrrolidon), poly(2-hydroxy ethyl methacrylate), poly(acrylicacid), poly(ethylene-co-vinyl acetate, poly(ethylene glycol),poly(methacrylic acid), and polyacrylamide;

(ii) bioresorbable polymers such as polylactides (PLA), polyglycolides(PGA), poly(lactide-co-glycolides) (PLGA), polyanhydrides, andpolyorthoesters;

(iii) natural polymers such as polysaccharides, collagens, silk,elastin, keratin, albumin, and fibrin; and

(iv) mixtures and combinations thereof.

In another alternative for making a shaped solid device, thesuperabsorbent polymers may be mixed with a solvent. The resultingsolution may be cast into the shaped solid device and the solventremoved by evaporation, optionally accompanied by heating.

Implanting the solid superabsorbent polymer device may compriseinserting a needle/trocar assembly into the intervertebral disc space,preferably such that the inserted end of the trocar is inside thenucleus pulposus of an intervertebral disc. One or more solid bodies maybe placed in the needle/trocar assembly and advanced or pushed throughthe assembly into the disc space. For example, a stylet or blunt needlemay be used to push the solid bodies through the needle/trocar assemblyand into the disc space. The needle/trocar then may be removed and thesolid device left behind in the disc space. Implanting alternatively maycomprise forming an aperture into the intervertebral space of themammal, and pushing a solid body implant(s) through the aperture andinto the intervertebral disc space. Fluoroscopy techniques may be usedto guide implantation of the solid device, if desired.

Delivery of the superabsorbent polymer to the disc space in the form ofa solid device is illustrated by way of example in FIG. 2, embodimentsA, B, C, and D. In embodiment A, a delivery device 24 (e.g., a syringeassembly) containing superabsorbent polymer pieces 25 a in the form ofsolid shaped devices, in this case small-diameter rods, is illustrated.The delivery device 24 pierces the annulus fibrosis 22 of theintervertebral disc space 20, which also comprises upper 21 a and lower21 b vertebral end plates. Preferably, as shown in embodiment A of FIG.2, the distal end of the delivery device pierces the nucleus pulposus 23of the intervertebral disc in order to directly deliver thesuperabsorbent polymer pieces into the nucleus.

As shown in embodiment B, the delivery device 24 may be depressed orotherwise activated in order to expel the superabsorbent polymer pieces25 b into the nucleus pulposus 23. As shown in embodiment C, thedelivery device 24 may expel multiple superabsorbent polymer pieces 25 binto the nucleus pulpous 23. However, it should be appreciated that, ifdesired, only a single superabsorbent polymer piece may be delivered tothe disc space. Preferably, sufficient superabsorbent polymer isdelivered to the disc space to substantially rehydrate the disc andincrease the disc space height, volume, and/or intra-discal pressure.

Embodiment D shows that the delivery device 24 may be removed from thedisc space upon delivery of the desired superabsorbent polymer pieces 25b. A hole or defect 26 may be left in the annulus fibrosis upon removalof the delivery device 24. As discussed herein, the defect in theannulus, if desired, may be closed using a subsequent treatment. Thismay be desirable in order to ensure that the water that is attracted tothe disc space by the highly hydrophilic superabsorbent polymer will beretained by the annulus and not allowed to readily exit the disc space.

An X-ray marker optionally may be included in the solid device. TheX-ray marker may be used to identify the solid device using fluoroscopytechniques in order to guide delivery of the device into theintervertebral disc. For example, a surgeon may use an appropriatefluoroscopy technique to guide delivery of the solid device directlyinto the nucleus pulposus of the intervertebral disc. The X-ray markermay comprise any appropriate material detectable by X-ray such as bariumsulfate, platinum, tungsten, tantalum, and other bio-compatiblematerials.

Whether using the “wet” or “dry” delivery methods, it is anticipatedthat the delivery device may form a puncture, hole, prick, etc.,preferably relatively small in size (e.g. ˜1 mm in diameter), in theannulus fibrosis in order to deliver the superabsorbent polymer materialinto the disc space. If desired, the puncture, hole, prick, etc. in theannulus fibrosis may be closed using additional treatment methods. Forexample, the application of energy via light, heat, or ultrasound may beused to cause the collagen fibers of the annulus to shrink and seal thehole. Alternatively, an occlusion device such as a plug or patch may beused to seal the hole. The occlusion device may be an in vivo formeddevice or an externally fabricated device that is subsequentlysurgically placed, preferably using minimally invasive surgicaltechniques, at the annulus fibrosis. A suitable tissue adhesive orsealant also may be used alone, or together with a plug or patch, toseal the defect in the nucleus. One skilled in the art will appreciatestill other techniques by which the hole in the annulus may be treatedin order to help ensure proper and speedy healing thereof.

In alternative embodiments, the delivery device may reach theintervertebral disc space via an intrapedicle route. This may bedesirable to completely avoid any potential damage to the annulusfibrosis. If needed, a small hole or tap may be drilled in an adjacentvertebral body to facilitate delivery of the superabsorbent polymers bythe delivery device. Preferably, however, a bone-piercing deliverydevice (e.g., certain syringes and needle assemblies are capable ofpiercing bone) may be used to deliver the superabsorbent polymers via anintrapedicle route. Similar devices and techniques are used invertebroplasty procedures, and one of skill in the art will appreciatehow the vertebroplasty procedures may be adopted to the delivery of asuperabsorbent polymer to the disc space, in accordance with theembodiments herein.

When delivering the superabsorbent materials either through anintrapedicle route or through the annulus, preferably an opening of nomore than about 5 mm is created in the endplate or annulus. Morepreferably, an opening of no more than about 3 mm is created in theendplate or annulus. Most preferably, an opening of no more than about 1mm is created in the endplate or annulus. As has been discussed withparticular reference to the annulus, the creation of passages oropenings leading to the intervertebral disc desirably is minimized inorder to ensure that the superabsorbent polymers that are delivered tothe disc space, the water that is attracted to and retained in the discspace by the superabsorbent polymers, and the nucleus pulposus is notable to easily exit the disc space. Therefore, the openings preferablyare minimal in number (e.g., preferably only one) and preferably areminimal in size (e.g., preferably only 1 mm or less).

Additionally, whether using “wet” or “dry” delivery methods, it may bedesirable to introduce an aqueous solution to the disc space and/ornucleus pulposus following delivery of the superabsorbent polymermaterial to the disc. Normally, it would be expected that water would beattracted by the highly hydrophilic superabsorbent polymers to theintervertebral disc space via natural routes to the disc space such asseeping through the annulus and micropores in the vertebral endplatesand adjacent vertebral bodies. However, it may be desirable toaccelerate the rehydration process by directly introducing an aqueoussolution to the disc space. For example, a separate delivery device suchas a syringe may be used to puncture the annulus and deliver water or abuffered saline solution directly to the disc space.

In further embodiments, various additives may be delivered to the discspace prior to, concurrently with, or subsequent to delivery of thesuperabsorbent polymers. Additives contemplated for delivery to the discspace include, but are not limited to:

(i) proteoglycans to replace or augment the proteoglycans of the nucleuspulposus;

(ii) growth factors such as transforming growth faction (TGF)-beta, bonemorphogenic proteins (BMPs), fibroblast growth factors such as acidicand basic fibroblast growth factor (FGF-1 and -2), platelet-derivedgrowth factors (PDGF) such as PDGF-AB, PDGF-BB, and PDGF-AA,insulin-like growth factors (IGF) such as IGF-I and -II, anti-TNF alpha,lymphokines, FGF-1, FGF-2, FGF4, PDGFs, EGFs, IGFs, OP-1,osteoid-inducing factor (OIF), angiogenin(s), endothelins, hepatocytegrowth factor, keratinocyte growth factor, osteogenin (bonemorphogenetic protein-3), HBGF- and -2, growth differentiation factors(GDF's), members of the interleukin (IL) family such as IL-1 to IL-6,members of the colony-stimulating factor (CSF) family such as CSF-1,G-CSF, and GM-CSF, and members of the hedgehog family of proteins,including indian, sonic and desert hedgehog;

(iii) cells such as disc cells, annulus cells, nucleus cells,chondrocytes, fibroblasts, nochordal cells, fibroblasts, chondrocytes,and mesenchymal stem cells;

(iv) radiocontrast media such as iodine-containing radiographic contrastagents (e.g., OMNIPAQUE® and HYPAQUE®, both available from AmershamHealth, Amersham, United Kingdom);

(v) organic polymers such as polyurethane, polyester, silicone,polyolefin, polyethylene, polyetheretherketone (PEEK),silicone-polyurethane copolymers, polyolefin, polyester, polyethyleneoxide, polyethylene glycol, poly(dioxanone), poly(β-caprolactone),poly(hydroxylbutyrate), poly(hydroxylvalerate), tyrosine-basedpolycarbonate, and polypropylene fumarate;

(vi) carbohydrates, starches, and polysaccharides such as carboxymethylcellulose, chitin, chitosan, agar, chondroitin sulfate, dermatansulfate, keratan sulfate, heparan, heparan sulfate, dextran, dextransulfate, alginate, and hyaluronic acid

(vii) crosslinking agents such as:

-   -   polyfunctional ethylenically unsaturated cross-linking agents        such as N,N′-methylenebisacrylamide, polyethylene glycol        di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and        divinyl benzene;    -   polyfunctional cross-linking agents such as epichlorohydrin and        related halo epoxy compounds, diglycidyl ether compounds,        diisocyanates, polyaldehydes, and polyfunctional amines and        imines;    -   triallylamine, diaziridine compounds, acrylic acid,        diiodopropane, dichloropropane, ethylene glycol diglycidyl        ether, alkylenebisacylamides, di- and poly-halogenated        compounds, and di- or poly-epoxy compounds;

(viii) peptides and proteins such as collagen, gelatin, silk, elastin,keratin, albumin, glycoproteins, lipoproteins, and fibrin; and

(ix) other drugs, analgesic compounds, anesthetics, antibacterialcompounds, antibiotics such as tetracycline and ciprofloxacin,antibodies, antifungal compounds such as diflucan, ketaconizole andnystatin, anti-inflammatories such as α-1-anti-trypsin andα-1-antichymotrypsin, antiparasitic compounds such as pentamidine,antiproliferative/cytotoxic drugs such as 5-fluorouracil (5-FU) andtaxol, antiviral compounds such as gangcyclovir, zidovudine, amantidine,vidarabine, ribaravin, trifluridine, acyclovir, and dideoxyuridine,anticancer compounds, cytokines such as α- or β- or γ-Interferon,genetic agents, enzyme inhibitors, hormones, steroids,glucocorticosteroids, immunomodulators, immunoglobulins, minerals,neuroleptics, oligonucleotides, peptides, tumoricidal compounds,tumorstatic compounds, toxins, vitamins and other nutritionalsupplements, as well as mixtures and combinations of the above-mentionedadditives.

As mentioned, cross-linking agents may be included as an additive duringdelivery of the superabsorbent polymers to the intervertebral discspace. According to the present methods, the superabsorbent polymers maybe at least partially crosslinked prior to delivery to the disc space.In other words, the present methods contemplate that the superabsorbentpolymers may be crosslinked to form small particulate polymer beads,fibers, flakes, granules, microspheres, nano-particles, particles,pellets, platelets, powder, randomly shaped particles, rods, chunks, orpieces prior to delivery to the disc space. Inclusion of a crosslinkingagent with the particulate superabsorbent polymer when it is deliveredto the disc space may result in crosslinking between and/or among theSAP particulate matter and other additives. This crosslinking may resultin the formation of an aggregate, cross-linked material in the discspace, the aggregate comprising the superabsorbent polymer(s) andoptional additive(s) cross-linked by the crosslinking agent(s). Thiscrosslinking may include physical, chemical, ionic, hydrogen-bonding,and/or other forms of crosslinking.

The methods described herein offer several advantages over nucleusreplacement, disc replacement, intervertebral fusion, and vertebralfixation procedures. Unlike vertebral fusion and vertebral fixationprocedures, rehydration of the nucleus and intervertebral disc spaceallows the disc to be retained and function in its intended fashion—asan articular joint that both absorbs loads placed on it by the spinalcolumn and permits flexation and rotation of the spinal column.Additionally, vertebral fixation is known to result in stress shieldingand stress localization, which may be avoided using the present methods.

The present methods also allow the disc nucleus and annulus to beretained, unlike nucleus replacement and disc replacement procedures. Inthe present methods, preferably no cutting of the annulus fibrosis orremoval of the nucleus occurs. Therefore, there is a decreasedlikelihood that a large defect would be created in the annulus fibrosisor endplates, which are known to heal only slowly and are not generallycapable of being healed after massive trauma. Preferably, the onlycompromise of the annulus fibrosis that occurs in utilization of thepresent methods is a small needle prick or hole to insert a cannula orother such device into the disc space in order to deliver thesuperabsorbent polymer. Furthermore, implantation of nucleus replacementdevices typically require comparatively large (e.g., 5 mm-12 mm) holesin the annulus for passage of the device. The present methods allowsuperabsorbent polymers to be delivered to the disc space throughcomparatively small (e.g., 1 mm-3 mm) holes in the annulus. Again, thismay decrease the likelihood of inflicting permanent injury to theannulus when treating a degenerated or dehydrated intervertebral disc.

A further benefit of the present methods is that removal of the annulusand/or nucleus may result in additional loss of joint strength becauseof the cutting and removal required. This additional loss of jointstrength may result in a substantial weakening of the disc space thatcannot be compensated for in terms of mechanical support andfunctionality. Comparatively, the present methods enable the retentionof the nucleus and annulus, and therefore preferably will not result inany further destabilization of the disc space, even if thesuperabsorbent polymers do not provide the level of rehydration andbulking effects that are hoped for.

Additionally, unlike nucleus replacement and disc replacement devices,the superabsorbent polymers of the present methods preferably do notbear a significant amount of the load placed on the intervertebral discby the spinal column. Instead, as described herein, the load preferablyis born by the rehydrated nucleus and the annulus fibrosis, as wouldoccur in a healthy, normal intervertebral disc. Nucleus and discreplacement devices, in comparison, bear a substantial, if not all, ofthe load placed on the intervertebral disc and must therefore themselvesbe of sufficient strength and rigidity to function as intended.

Furthermore, the present methods may be utilized in embodiments whereinthe nucleus pulposus and annulus fibrosis are retained. This isadvantageous as a simplified procedure compared to the implantation ofnucleus and disc replacement devices that may require removal of thenucleus and annulus. For example, the present methods may beaccomplished using minimally invasive surgical techniques. Additionally,the present methods may be accomplished using a percutaneous approach tothe disc space. These advantages may make the present methods especiallydesirable for conservative care patients with back or neck pain that arenot receptive to surgical intervention. Alternatively, however, some orall of the nucleus and annulus of the intervertebral disc that is to betreated with the present methods may be removed prior to, during, orsubsequent to performing the present methods on the disc space. Removalof a portion or all of the nucleus or annulus may be especiallydesirable where at least a portion of the nucleus or annulus is damaged.

Also, superabsorbent polymers preferably may be delivered to the discspace in accordance with the present methods with or without in-situcrosslinking of the superabsorbent polymers. The present methodsadditionally contemplate that the superabsorbent polymers may be atleast partially crosslinked prior to delivery to the disc space. Inother words, the present methods contemplate that the superabsorbentpolymers may be crosslinked to form small particulate polymer beads,fibers, flakes, granules, microspheres, nano-particles, particles,pellets, platelets, powder, randomly shaped particles, rods, chunks, orpieces prior to delivery to the disc space. These particulatesuperabsorbent polymers then may be delivered to the disc spaceaccording to the “wet” and “dry” delivery methods described herein. Thisis unlike the injection of liquid hydrogel-precursor solutions into theintervertebral disc space, because the liquid hydrogel-precursorsolutions typically are not crosslinked prior to delivery to the discspace, and undergo significant in-situ crosslinking subsequent todelivery.

Still another benefit of the present methods is the possible restorationof intra-discal pressure. It is believed that, through the osmoticpressure, or hydrophilic action, of the superabsorbent polymer, watermay be attracted to and retained in the intervertebral disc space. Thismay lead to an increase in intra-discal pressure, and preferably to arestoration of intra-discal pressure to its normal state. Intra-discalpressure it thought to be important not only to the basic functioning ofthe intervertebral disc, but to its general health also. Notably, areduced intra-discal pressure may lead to destabilization anddeterioration of the annulus fibrosis. Therefore, the present methodsare thought to reduce the rate of progressive annulus deterioration inan under-inflated intervertebral disc.

The present methods may be used multiple times for treating patientswith intervertebral discs that are in need of rehydration. As describedherein, the methods provided by the present embodiments may beparticularly appropriate to treat mild to moderate degeneration of theintervertebral disc. Following initial treatment with a superabsorbentpolymer, subsequent treatment may be periodically scheduled or treatmentmay be repeated when the disc has again degenerated to the point ofrequiring additional augmentation or treatment.

Another embodiment provides for the use of an inflatable member toaugment and rehydrate a nucleus pulposus of an intervertebral disc. Inthis embodiment, an inflatable member is inserted into a dilated openingin an intact intervertebral disc annulus and into a nucleus pulposus ofthe disc. The inflatable member is inserted into the nucleus pulposus ina deflated state, and is connected to an inflation device tocontrollably inflate the inflatable member within the nucleus pulposus.A superabsorbent polymer material is delivered to the inflatable memberby means of the inflation device. Sufficient superabsorbent polymer maybe delivered to the inflatable member to cause full, or only partial, orno inflation of the member. Preferably, the superabsorbent polymer isdelivered to the inflatable member in a relatively dry state, and thenabsorbs water after delivery to cause further expansion of theinflatable member. The nucleus pulposus of the intervertebral disc maybe either removed or retained, in part or in whole, in this embodiment.

Alternatively, the superabsorbent polymer may be delivered to theinflatable member during or before implantation of the inflatable memberin the disc space. In this embodiment, the superabsorbent polymerpreferably is delivered to the inflatable member in a dry or partiallyhydrated state so that the volume of the inflatable member with thesuperabsorbent polymer inside of it is minimized during implantation.

The inflatable member filled with superabsorbent polymer materialdesirably causes the nucleus pulposus of the intervertebral disc toexpand. In one embodiment, the inflatable member impacts the vertebralend plates of the disc space directly, thereby dilating the end platesand expanding the disc space. In another embodiment, the inflatablemember does not impact the vertebral end plates of the disc spacedirectly, and therefore causes expansion of the disc space onlyindirectly via expansion of the nucleus pulposus into which theinflatable member is implanted. In either case, the inflatable memberfilled with a superabsorbent polymer and left in a disc space as apermanent implant may cause expansion of the disc space to at leastpartially restore lost disc height, disc volume, and/or intra-discalpressure.

Preferably, the inflatable member is porous or permeable (e.g., wovenfabric, mesh structure, perforated membrane, etc.) in order to allowfluids, such as bodily fluids and aqueous solutions delivered to theintervertebral disc space, to enter the inflatable member. In this way,water may reach the superabsorbent polymer within the inflatable member,causing further expansion of the inflatable member. In anotherembodiment, aqueous solutions may be delivered directly to theinflatable member by means of another needle or catheter, in order tocause further expansion of the superabsorbent polymer within theinflatable member.

In order to inject the superabsorbent polymer into the inflatablemember, it may be necessary to fluidize the polymer material. Forexample, the superabsorbent polymer may be heated in order to reduce itsviscosity such that it becomes sufficiently fluid for injection into theinflatable member. In another embodiment, the superabsorbent polymer maybe mixed with a solvent in order to fluidize the polymer. For example,the solvents previously mentioned including water, saline, alcohol,glycerin, ethylene glycol, dimethyl sulfoxide (DMSO), mineral oil,silicone oil, vegetable oil (e.g., canola, corn, and peanut oil), oliveoil, and so forth may be used to fluidize the superabsorbent polymer forinjection into the inflatable member. Preferably, a non-aqueous solventis used to fluidize the superabsorbent polymer in order to avoidsignificant expansion of the polymer before injection into theinflatable member.

The inflatable member may take the form of a balloon of various shapessuch as conical, spherical, square, long conical, long spherical, longsquare, tapered, stepped, dog bone, offset, and combinations thereof.Balloons can be made of various polymeric materials such as polyethyleneterephthalates, polyolefins, polyurethanes, nylon, polyvinyl chloride,silicone, polyetheretherketone, polylactide, polyglycolide,poly(lactide-co-glycolide), poly(dioxanone), poly(ε-caprolactone),poly(hydroxylbutyrate), poly(hydroxylvalerate), tyrosine-basedpolycarbonate, polypropylene fumarate, and combinations thereof.

The inflatable member may be delivered to the disc space and inflatedwith the superabsorbent polymer in a number of different ways. Forexample, one embodiment provides an apparatus including a high-pressureballoon catheter (i.e., the inflatable member) with a small shaftdiameter (3 mm or smaller, preferably 2 mm or smaller, and mostpreferably 1 mm or smaller). The catheter has a pointed tip forpuncturing an intact disc annulus and inserting the balloon section intothe nuclear pulposus region. The catheter either has a rigid shaft or issupported by a rigid guide-needle during penetration into the disc. Fora rigid shaft, the catheter can be made of metal tubing. For a flexibleshaft, the catheter can be made of polymeric tubing and is supportedwith a rigid guide-needle or guide-wire. If a guide-needle is used, thecatheter can be double lumen. The balloon has an appropriate finalvolume of from about 0.1 mL to about 8.0 mL, preferably up to 5.0 mL anddimensions (length from about 5 mm to about 40 mm, preferably from about10 mm to about 30 mm; and diameter from about 3 mm to about 20 mm,preferably from about 5 mm to about 15 mm) to fit in the nuclearpulposus region of the intervertebral disc.

FIG. 3, embodiments A and B, depicts an exemplary method for treatmentof an intervertebral disc space using an inflatable member and asuperabsorbent polymer. The disc space 30 comprises endplates 31 a and31 b, annulus fibrosis 32, and nucleus pulposus 33. A cannula 34 isconnected to an inflatable member 35 that is inserted into the discspace, in this case into the nucleus 33. As shown in embodiment A, theinflatable member 35 may be inserted into the disc space in ansubstantially deflated form. Then, as shown in embodiment B, asuperabsorbent polymer 36 may be injected into the inflatable member 35,for example, via the cannula 34. The superabsorbent polymer 36 may causethe inflatable member 35 to expand to an in-dwelling shape.

In another exemplary balloon catheter, a double lumen balloon cathetercan be used for delivery and injection of the balloon. The double lumenballoon catheter includes a first channel, a second channel, and aballoon. The superabsorbent polymer is injected into the balloon via thefirst channel to inflate balloon for expansion of the disc nucleus.Bodily fluids may reach the superabsorbent polymer inside of theinflatable member by permeating the inflatable member. Alternatively orin conjunction with permeation of bodily fluids, aqueous solutions maybe delivered to the superabsorbent polymer directly via the firstchannel of the double lumen balloon catheter or by injection into theinflatable member using a separate needle/cannula. The balloon then maybe detached from the catheter and left inside of the nucleus pulposuswhen the catheter is withdrawn from the disc space.

Another embodiment provides a method for rehydrating or augmenting anintervertebral disc comprising first determining that the treated dischas a competent and intact annulus fibrosis for safe expansion andeffective containment of the subsequently injected superabsorbentpolymer. After the annulus quality and integrity are verified, forexample using discography, the inflatable member is inserted into thecenter of the disc. Insertion of the inflatable member can be donepercutaneously, preferably under fluoroscopic guidance. The inflatablemember then is inflated with radio-contrast fluid or saline topressurize the disc, and thereby, stretch the annulus fibrosis. After apredetermined inflation time, the balloon is deflated and removed fromthe disc space. The superabsorbent polymer subsequently is injected intothe disc using a small-diameter hypodermic needle until a desirableinjection volume is achieved. If desired, an aqueous solution also maybe delivered to the superabsorbent polymer. The entire procedurepreferably is done under fluoroscopic guidance.

Methods of treating an intervertebral disc using inflatable members aredisclosed in U.S. Patent Application Publication No. 2004/0186471, thedisclosure of which is incorporated herein by reference in its entirety.In a present embodiment, the superabsorbent polymers provided herein maybe used to inflate the inflatable member in accordance with the variousembodiments and methods disclosed in the '471 application. Furtherembodiments herein provide that the inflatable members andsuperabsorbent polymers may be used, for example, as a compliant core ina total disc replacement device, a nucleus replacement device, as adevice to augment a facet joint, as a spacer for separation ofinterspinous processes, as a filler in expandable spinal rods forpartial or full spinal stabilization, and other such embodiments.

The foregoing detailed description is provided to describe theembodiments in detail, and is not intended to limit them. Those skilledin the art will appreciate that various modifications may be made to theembodiments without departing significantly from the spirit and scopethereof.

1. A method for treating an intervertebral disc having a nucleuspulposus and an annulus fibrosis, using one or more superabsorbentpolymers, comprising introducing the superabsorbent polymers into theintervertebral disc space without removing nucleus pulposus or annulusfibrosis material, thereby rehydrating the intervertebral disc space. 2.The method of claim 1, wherein the intervertebral disc is rehydrateduntil equilibrium swelling is attained.
 3. The method of claim 1,wherein the intervertebral disc is at least partially collapsed, andtreating the intervertebral disc increases the intervertebral disc'sheight.
 4. The method of claim 1, wherein the intervertebral disc isexperiencing progressive disc collapse, and treating the intervertebraldisc decreases the rate of disc collapse.
 5. The method of claim 1,wherein the intervertebral disc is experiencing progressive disccollapse, and treating the intervertebral disc maintains theintervertebral disc's height.
 6. The method of claim 1, wherein thesuperabsorbent polymers are not more than about 30% crosslinked.
 7. Themethod of claim 6, wherein the superabsorbent polymers are not more thanabout 10% crosslinked.
 8. The method of claim 1, wherein thesuperabsorbent polymers are capable of absorbing an amount of fluid atleast about ten times the weight of the superabsorbent polymers in theirdry form under atmospheric pressure.
 9. The method of claim 8, whereinthe superabsorbent polymers are capable of absorbing an amount of fluidat least about twenty times the weight of the superabsorbent polymers intheir dry form under atmospheric pressure.
 10. The method of claim 1,wherein the superabsorbent polymers are in one or more forms selectedfrom the group consisting of beads, fibers, flakes, granules,microspheres, nano-particles, particles, pellets, platelets, powder,randomly shaped particles, rods, chunks, and pieces.
 11. The method ofclaim 1, additionally comprising introducing fluids into theintervertebral disc.
 12. The method of claim 1, additionally comprisingintroducing one or more additives into the intervertebral disc.
 13. Themethod of claim 12, wherein the additives are selected from the groupconsisting of analgesic compounds, anesthetics, antibacterial compounds,antibiotics, antibodies, antifungal compounds, anti-inflammatories,antiparasitic compounds, antiviral compounds, anticancer compounds,carbohydrates, cells, crosslinking agents, cytokines, drugs, geneticagents, enzyme inhibitors, hormones, steroids, glucocorticosteroids,growth factors, immunoglobulins, immunomodulators, lipoproteins,minerals, neuroleptics, nutritional supplements, oligonucleotides,organic polymers, peptides, polysaccharides, proteins, proteoglycans,radiocontrast media, toxins, tumoricidal compounds, tumorstaticcompounds, and vitamins.
 14. The method of claim 1, wherein introducingf the superabsorbent polymers into the intervertebral disc spacecomprises: mixing the superabsorbent polymers with a medium to make thesuperabsorbent polymers flowable; and using a delivery device to injectthe flowable superabsorbent polymers into the disc space.
 15. The methodof claim 1, wherein introducing the superabsorbent polymers into theintervertebral disc space comprises: loading the superabsorbent polymersinto a delivery device; and using a plunger to force the superabsorbentpolymers from the delivery device into the disc space.
 16. The method ofclaim 1, wherein introducing the superabsorbent polymers into theintervertebral disc comprises: inserting an inflatable member into thedisc space; and using a delivery device to inject the superabsorbentpolymers into the inflatable member.
 17. The method of claim 16, whereinthe inflatable member is a balloon.
 18. The method of claim 17, whereinthe balloon is made of a polymer selected from the group consisting ofpolyethylene terephthalates, polyolefins, polyurethanes, nylon,polyvinyl chloride, silicone, polyetheretherketone, polylactide,polyglycolide, poly(lactide-co-glycolide), poly(dioxanone),poly(ε-caprolactone), poly(hydroxylbutyrate), poly(hydroxylvalerate),tyrosine-based polycarbonate, polypropylene fumarate.
 19. The method ofclaim 17, wherein the balloon is in a shape selected from the groupconsisting of conical, spherical, square, long conical, long spherical,long square, tapered, stepped, dog bone, and offset.
 20. The method ofclaim 16, wherein the inflatable member is permeable, semi-permeable, orimpermeable.
 21. A method for bulking up an intervertebral disc having anucleus pulposus and an annulus fibrosis, using one or moresuperabsorbent polymers, comprising introducing the superabsorbentpolymers into the intervertebral disc space without removing nucleuspulposus or annulus fibrosis material, thereby accomplishing at leastone of an increase in the disc height, an increase in the disc volume,and an increase in the intra-discal pressure.
 22. The method of claim21, wherein the intervertebral disc is rehydrated until equilibriumswelling is attained.
 23. The method of claim 21, wherein theintervertebral disc is at least partially collapsed and bulking up theintervertebral disc increases the intervertebral disc's height.
 24. Themethod of claim 21, wherein the intervertebral disc is experiencingprogressive disc collapse, and bulking up the intervertebral discdecreases the rate of disc collapse.
 25. The method of claim 21, whereinthe intervertebral disc is experiencing disc progressive collapse, andbulking up the intervertebral disc maintains the intervertebral disc'sheight.
 26. The method of claim 21 wherein the superabsorbent polymersare not more than about 30% crosslinked.
 27. The method of claim 26,wherein the superabsorbent polymers are not more than about 10%crosslinked.
 28. The method of claim 21, wherein the superabsorbentpolymers are capable of absorbing an amount of fluid at least about tentimes the weight of the superabsorbent polymers in their dry form underatmospheric pressure.
 29. The method of claim 28, wherein thesuperabsorbent polymers are capable of absorbing an amount of fluid atleast about twenty times the weight of the superabsorbent polymers intheir dry form under atmospheric pressure.
 30. The method of claim 21,wherein the superabsorbent polymers are in one or more forms selectedfrom the group consisting of beads, fibers, flakes, granules,microspheres, nano-particles, particles, pellets, platelets, powder,randomly shaped particles, rods, chunks, and pieces.
 31. The method ofclaim 21, further comprising introducing fluids into the intervertebraldisc.
 32. The method of claim 21, further comprising introducing one ormore additives into the intervertebral disc space.
 33. The method ofclaim 32, wherein the additives are selected from the group consistingof analgesic compounds, anesthetics, antibacterial compounds,antibiotics, antibodies, antifungal compounds, anti-inflammatories,antiparasitic compounds, antiviral compounds, anticancer compounds,carbohydrates, cells, crosslinking agents, cytokines, drugs, geneticagents, enzyme inhibitors, hormones, steroids, glucocorticosteroids,growth factors, immunoglobulins, immunomodulators, lipoproteins,minerals, neuroleptics, nutritional supplements, oligonucleotides,organic polymers, peptides, polysaccharides, proteins, proteoglycans,radiocontrast media, toxins, tumoricidal compounds, tumorstaticcompounds, and vitamins.
 34. The method of claim 21, wherein introducingthe superabsorbent polymers into the intervertebral disc spacecomprises: mixing the superabsorbent polymers with a medium to make thesuperabsorbent polymers flowable; and using a delivery device to injectthe flowable superabsorbent polymers into the disc space.
 35. The methodof claim 21, wherein introducing the superabsorbent polymers into theintervertebral disc space comprises: loading the superabsorbent polymersinto a delivery device; and using a plunger to force the superabsorbentpolymers from the delivery device into the disc space.
 36. The method ofclaim 21, wherein introducing the superabsorbent polymers into theintervertebral disc comprises: inserting an inflatable member into thedisc space; and using a delivery device to inject the superabsorbentpolymers into the inflatable member.
 37. The method of claim 36, whereinthe inflatable member is a balloon.
 38. The method of claim 37, whereinthe balloon is made of a polymer selected from the group consisting ofpolyethylene terephthalates, polyolefins, polyurethanes, nylon,polyvinyl chloride, silicone, polyetheretherketone, polylactide,polyglycolide, poly(lactide-co-glycolide), poly(dioxanone),poly(ε-caprolactone), poly(hydroxylbutyrate), poly(hydroxylvalerate),tyrosine-based polycarbonate, polypropylene fumarate.
 39. The method ofclaim 37, wherein the balloon is in a shape selected from the groupconsisting of conical, spherical, square, long conical, long spherical,long square, tapered, stepped, dog bone, and offset.
 40. The method ofclaim 36, wherein the inflatable member is permeable, semi-permeable, orimpermeable.